The presence of atherosclerotic plaque on the walls of blood vessels narrows the lumen of the blood vessel and reduces the flow of blood to downstream tissues. This is a particularly serious problem when the narrowing or stenosis is located in the blood vessels which provide nutrient blood to the muscles of the heart. The presence of such coronary stenotic lesions is a major predisposing factor in both acute and chronic heart problems.
Over the last decade the medical procedure known as percutaneous transluminal coronary angioplasty (PTCA) has become widely accepted as a safe and effective method for treating vascular conditions resulting from plaque formation in the coronary arteries and, to a lesser extent, in other vascular locations. Typically, this procedure utilizes a dilation catheter having an inflatable balloon at its distal end. Using a fluoroscope and radiopaque dyes for visualization, the balloon is guided into position across the stenosis and inflated for a brief period to collapse or displace the stenotic lesion in order to open the artery and reestablish adequate blood flow. A wide variety of balloon catheter designs have evolved in recent years in order to provide the vascular physician with the ability to access lesions at previously inaccessible locations along the tortuously branched pathways of the coronary arteries. Of equal importance, balloon catheters have been developed which enable the vascular physician to re-cross a vascular lesion following an initial balloon angioplasty in the event it is necessary to reopen a particularly difficult or complicated lesion.
Although relatively uncommon in PTCA, complications do arise which may require further attention by the physician. For example, cases of acute reclosure have been noted where a blood vessel will dramatically restrict or even close completely following balloon angioplasty. Typically, such acute reclosure will result from a portion of the compressed or displaced stenotic lesion breaking free from the vascular endothelium and projecting into the blood flow decreasing blood flow and providing a possible location for blood clot development. Alternatively, muscular spasms within the arterial walls following angioplasty may constrict the blood vessel around the site of the lesion to a point that effectively shuts off blood flow.
Where available, the current procedure for dealing with such cases of acute reclosure involves recrossing the stenotic lesion with a balloon catheter and reinflating the balloon for an extended period of time. In this manner, it is sometimes possible to reattach the atherosclerotic plaque to the wall of the artery and re-establish blood flow. Alternatively, a variety of shunts and stents have been developed for achieving the same purpose with varying degrees of success.
An additional complication that may be experienced in connection with PTCA is a phenomenon known as vascular dissection. In this situation, the tissues forming the wall of the blood vessel split or tear to varying degrees, weakening or perforating the vessel. It is again preferable then to re-cross the lesion with a stent or similar apparatus in an effort to support the damaged blood vessel while facilitating fusion of the dissection. Alternatively, more invasive forms of vascular surgery may be necessary to correct these complications.
Recently, alternative methodologies for opening restricted vascular pathways have been tested utilizing lasers and microwaves to deliver various amounts of energy to the site of stenosis. In laser angioplasty a light guide is inserted along the vascular pathway to the point of the stenosis and laser energy is utilized to vaporize the plaque forming the lesion. Microwave angioplasty utilizes a very flexible transmission line which is advanced along the vascular pathway to the site of the stenosis to deliver microwave energy which heats the atherosclerotic plaque and, theoretically softens the lesion prior to dilation with a balloon catheter. Neither of these techniques has met with much success utilizing existing technology. For example, it has proven difficult to access coronary lesions because the currently available light guides and microwave antenna/transmission lines are difficult to advance along the highly branched and convoluted pathways of the coronary arteries. Additionally, even where the stenotic lesions are readily accessible with existing devices it has proven to be difficult to effectively deliver sufficient amounts of energy to open or soften the lesion without producing unacceptable damage to the surrounding vascular tissues or to the equipment.
There are also other procedures where controlled application of energy promotes treatment of various conditions. For example, in cases of cardiac arrhythmia, localized application of thermal energy to nodal areas can often promote redevelopment of proper node structure. Other situations where delivery of a hyperthermic dose may provide beneficial treatment include treatment of vascular conditions such as other coronary artery disease, ablation of atherosclerotic plaque, and in treatment of conditions in other body cavities such as uterine and vaginal conditions.
Some device implantation procedures could also benefit from application of controlled amounts of energy. A vascular stent may be positioned by inserting the stent into the subject vessel using a catheter to properly locate the stent.
Accordingly, it is an object of present invention to provide an improved transmitter, for example of the microwave type, for use in connection with the opening of vascular lesions and the subsequent treatment of vascular conditions including acute reclosure, vascular dissection, cardiac arrhythmia, other coronary artery complications, treatment of conditions in body cavities such as uterine and vaginal conditions and for insertion of devices. In conjunction with these goals it is an object of the present invention to provide a microwave antenna or transmission cable which can be readily guided along tortuous pathways in order to provide access to lesions located in areas that were previously inaccessible to microwave treatment.
It is a further object of the present invention to provide an improved percutaneous transluminal microwave antenna which is sufficiently stiff in the axial direction to be pushable yet which retains a high degree of radial flexibility to facilitate steering and advancement along tortuous vascular pathways.
It is a still further object of the present invention to provide an improved percutaneous transluminal microwave antenna that will effectively deliver controlled amounts of energy to deeply treat target tissues.